Many processes in the semiconductor industry require a reliable source of process gases for a wide variety of applications. Often these gases are stored in cylinders or vessels and then delivered to the process under controlled conditions from the cylinder. The semiconductor manufacturing industry, for example, uses a number of hazardous specialty gases such as phosphine (PH3), arsine (AsH3), and boron trifluoride (BF3) for doping, etching, and thin-film deposition. These gases pose significant safety and environmental challenges due to their high toxicity and pyrophoricity (spontaneous flammability in air). In addition to the toxicity factor, many of these gases are compressed and liquefied for storage in cylinders under high pressure. Storage of toxic gases under high pressure in metal cylinders is often unacceptable because of the possibility of developing a leak or catastrophic rupture of the cylinder.
One recent approach to storage and delivery of Lewis acid and Lewis base gases (e.g., PH3, AsH3, and BF3) resides in the complexing of the Lewis base or Lewis acid in a reactive liquid of opposite Lewis character, e.g., an ionic liquid (e.g., a salt of alkylphosphonium or alkylammonium) of opposite Lewis character. Such liquid adduct complexes provide a safe, low pressure method of storage, transporting and handling highly toxic and volatile compounds.
The following reference illustrates a delivery system for Lewis basic and acidic gases from reactive liquids and proposed mechanisms for the formation of Lewis complexes of Lewis gases with reactive liquids and for recovering the gases from the reactive liquids and delivering the respective gases to the onsite facility:
US 2004/0206241 (the subject matter of which is incorporated by reference) discloses a system for storing Lewis base and Lewis acidic gases in a nonvolatile, reactive liquid having opposing Lewis acidity and Lewis basicity. Preferred systems employ the storage and delivery of arsine, phosphine and BF3 in an ionic liquid.